If you add in any excess amount of food into a tank and it is left uneaten it will eventually start to decompose and yes this will have an effect on your water peramiters. How great an effect depends on how great an amount is left to rot and how often you are adding to this problem.
Alright thanks. I wasn't sure if I could just keep it in there or not. Do you recommend just clipping it to the side of the tank or could I make some small pieces and drop them in the tank?
Clipping it will keep it in place. If it's not secure, the seaweed will just float and later on drift around your tank, possibly to behind your rockwork so it can decompose.
